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Q: We have a slow knocking sound coming from inside a wall. The sound occurs when the upstairs bathroom faucet is turned on. I have been told that this could be the pipes banging against the wall. Is this a serious problem? 

A: Knocking pipes aren’t usually a serious plumbing problem, but they can drive you nuts. 

Knocking or banging pipes can be caused by several factors; excessively high water pressure (over 55 psi), air in the water lines or a failing faucet washer. Sometimes the knocking radiates along hot water pipes from a sediment-laden water heater that is in need of flushing. However, the banging would occur at more than one faucet (not just the upstairs bathroom faucet, as you describe) if the source of the problem were any of the aforementioned. 

We have a hunch that the knocking is caused by vibration due to a brittle or deteriorating washer. If the faucet consists of two handles, try to determine whether the knocking occurs when using “hot” or “cold” water. 

Once you have narrowed it down to one or the other, close the shut-off valve (usually in the cabinet below the faucet) and remove the decorative handle, packing nut and valve stem. The washer is attached to the bottom of the valve stem with a small screw. Remove the existing washer and replace it. Reassemble the faucet in the reverse order that you took it apart. If your faucet is a “single-lever” model, remove the handle and packing nut as you would a two-handle model. However, instead of replacing a valve-stem washer, you will use a washer replacement kit. 

Q: How do I change a leaking toilet tank? 

A: The first step in repairing a leaking toilet tank is to determine where the leak is located and what is causing it. There are several possible causes, the most obvious of which is a hairline crack in the tank – often virtually undetectable. Other possible causes are the four factory penetrations at the bottom of the tank where connections are made to the water supply, where the tank is bolted to the bowl, and at the location where water flows from the tank to the bowl. 

Each of these locations has a rubber washer designed to ensure a watertight connection. An easy means of determining the location of the leak is by placing a few drops of food coloring into the toilet tank. Wait about an hour and return to the scene to search for colored water at the outside of the tank. If the leak is at one of the factory penetrations, use a wrench or screwdriver to tighten the connection. Dry the area and return in another hour to see if the problem has been solved. If not, try replacing the washers. 

Drain the tank by turning off the water supply and flushing the toilet. Disconnect the water supply and remove the two bolts that anchor the tank to the bowl.  

Before you get set on tearing out your toilet tank, be certain that your leak isn’t a sweating tank. 

A sweating tank is caused by condensation that occurs on the outside surface of the toilet tank due to the difference in temperature between the water in the toilet tank and the air in the room. If the problem is condensation, it can be remedied in one of two ways – with a tank liner or a tempering valve. 

The tank liner consists of a rubber membrane that is installed in the interior surface of the tank as a layer of insulation. The tempering valve is a bit more complicated. It requires removing the existing water supply valve and replacing it with a model that mixes a small amount of hot water so that the water in the tank isn’t so cold, thus eliminating condensation. The former is a common do-it-yourself project, whereas the latter often requires a plumber.